Why 7.62, not some even number?


What possessed people to develop weird calibre sizes like 7.62mm? Why not 7.60mm? What is the importance of that 0.02? Why not just make 8mm Mauser (8.00mm) since people refer to it as 8mm and not 7.92mm? Is this a logical calculated decision or originally someone just had a 7.62mm drill to make a barrel?


7,62mm are .30 inch. as 6,35mm is one quarter of an inch or 12,7mm is half inch


Ah, but then why do .30 bullets measure out to .308?


Yes, 7.62mm is .30 inch and it is a nice round number. But I don’t believe than European (non-British) gunmakers were looking to North America for gun design ideas and British measurement systems in late 1800’s. Germans, Belgians, Italians etc. were quite prolific themselves and they thought in millimetres not inches. So. again, why 7.62mm and not 7.60mm? I work in bio-medical manufacturing and when I am asked to make 99.87 litres of buffer solution, I make 100 litres. It is easier to calculate and do accounting.


Thanks to International Bureau for the Complication of the Easy Affairs


We all know why. The groove diameter is .308". The bore diameter is .300". Now, if someone made the groove diameter an even .300", someone would ask, “why did they make the bore diameter .292?”

If you take just about every dimension on just about every manufactured item you can ask the question, “why did they make it that way?” I have my own theory which is - that is just the way it came out. No particular reason or logic behind it. If you are an anal perfectionist it must drive you crazy. I’m sure there is a medical term to describe this but I don’t know what it is.



I am sorry to be anal, but let me re-phrase my question. If I ask you to install a new window in my house, and you suggest 4x6 foot window, it sounds reasonable to me. But if you say 4.6753 by 6.5397 feet, I’ll ask why. If I were to design a new rifle, I’d say lets make the bore 8.00mm and adjust cartridge size and amount of gun powder accordingly. There must have been a logical reason. I was just curious what it was.



My comment was a lot tongue in cheek and certainly wasn’t aimed at you or anybody else. I apologize if I offended anyone.

My point was that arriving at final dimensions for anything is seldom based on anything but what I said before. “Because that’s the way it came out.”

If you read some of the official reports from the late 1880s when Springfield Armory was investigating a smaller caliber rifle to replace the 45-70, you will be astonished at the reasoning behind why it was 30 caliber. Here’s a quote.

[color=red] “The even .30 caliber was chosen as being the smallest admissible, all things considered, not from any special principle involved, 7.5 and 8 millimeters being generally the calibers adopted abroad.”[/color]

So that’s how our Government arrived at the caliber of US Military small arms that prevails to this day.

I do a lot of my own gunsmithing and build my own rifles for Benchrest shooting. There are many times when I am fabricating a part that I will use non-standard dimensions on things such as threads, etc. I just know that someday, someone will disect one of my rifles and wonder, “Now why did the he use a .462” x 22 TPI thread to attach the compulator to the whatchcallit?" If I was alive, I would tell them, “Because that’s the way it came out.”

I believe that our world is a lot more random, even chaotic, than we would like to believe.



Thanks to International Bureau for the Complication of the Easy Affairs[/quote]
what I wrote was a joke. I hope that I do not said something offensive.


" It is a fool who looks for logic in the chambers of the human heart". Few decisions, even technical ones are logical. Most decisions are : 1)political,2)personal,3)economic. The adoption of official names even for weapons and weapons systems are political in nature. Why do we have the LAW tubes instead of the far more efficient Panzerfaust and RPG style weapons ? POLITICS. A 30cal bullet measures .308 and I have to click “start” to turn off my computer. German Mauser ammo is 7.9 in Germany,7.92 for export and 8mm here.


Hmm, just think of the poor general public when discussing this topic – cartridge “caliber” really tells so little about its purpose/power. A .22-250 is a .22, but so is a .22 rimfire (Aguila) Colibri. A .458 Win Mag is a “.45”, but so is a .455 Webley. These pairs are worlds apart, and the way these topics are discussed in the general media confuses the issue further still, rather than simplifying matters. Thankfully, this forum exists to clarify matters for the uninitiated, and help the most experienced collectors with some of the toughest questions. This subject is definitely not for those who expect all answers to be logically ordered and to fall into neat categories. Experience is the best guide, and even that fails us at times. Still, I have been able to get satisfactory answers to even my most challenging and esoteric questions.
I’m still a beginner at all this, and will be for the rest of my life, but I continue to learn. Oh, and thanks to all of you who have answered those questions, I do appreciate the time and knowledge that you have shared so freely.